A bear market in the S&P 500 — a decline of 20 percent or more from recent highs — would be a catalyst for an economic slowdown, according to Peter Boockvar, chief investment officer at Bleakley Advisory Group.

That kind of drop would alter consumer behavior, Boockvar told CNBC on Wednesday.

"You'll see consumers that are reining things in," he added. "You'll have CEOs and CFOs that say, 'You know what, market is down 20 percent, and I have limited visibility now.'"

The last S&P 500 bear market happened during the financial crisis when the index lost 56 percent of its value from the then-record high close of 1,565 on Oct. 9, 2007 to the closing low of 676 on March 9, 2009.

That means the current bull market — the longest since World War II — has been rolling ever since then.

However, some claim the bull market for all intents and purposes ended in October 2011 because on an intraday basis the S&P 500 fell 20 percent from its most recent high. But it did not close there, which would have had to happen to count it as a bear market under the generally accepted definition.

Wall Street is concerned about a possible inversion of the yield curve, which is when shorter term rates exceed longer term rates. The phenomenon has historically been a signal an economic slowdown ahead.

Needham Growth Fund portfolio manager Chris Retzler — appearing with Boockvar on CNBC Wednesday — said that "any inversion is concerning," but he does not see an economic recession on the horizon just yet.

U.S. stocks futures Wednesday bounced higher after Tuesday's steep losses on Wall Street. (Equity futures were scheduled to remain open until 9:30 a.m. ET, and to reopen Wednesday evening at 6 p.m. ET as normal.)

The New York Stock Exchange and the Nasdaq were closed Wednesday for the funeral of George H.W. Bush, the nation's 41st president. They reopen Thursday on a normal schedule. The U.S. Treasury market was also closed Wednesday.